Brake servos of the generic type are known, for example, from DE 103 33 983 A1 and DE 10 2008 037 048 A1, which are incorporated by reference, describing a conventional brake servo and DE 10 2008 037 048 A1 describing what is known as an active brake servo which can also be actuated by an electromagnet independently of an input member.
In modern vehicles, in particular, the automotive industry makes high requirements in relation to the acoustic comfort of the motor vehicle components. Said requirements cannot be met in part by way of the known brake servos. In tests, the provision of a high vacuum has proven to be a cause for disruptive noise emission. This occurs, inter alia, in the use of vacuum pumps which are necessary, in particular, in vehicles with an electric or hybrid drive, since no vacuum or insufficient vacuum can be provided by the motor/engine.
The high vacuum results in stick/slip effects and dynamic effects, in particular on the sealing ring for sealing the working chamber with respect to atmosphere, by way of which effects disruptive noises are produced.
It is therefore an aim of the invention to provide a brake servo, in which the described disadvantages can be avoided.
In order to achieve this, it is therefore proposed according to aspects of the invention that means are provided, in order, at the beginning of an actuation of the brake servo, to reduce an actively loaded area of the movable wall by division of the working chamber into a prechamber and a main chamber. As a result of the decrease in size of the working chamber in relation to the prechamber at the beginning of the actuation, a higher pressure difference is produced by way of the smaller, actively loaded area of the movable wall, which higher pressure difference ensures the sealing ring breaks free. Stick/slip effects and dynamic effects can therefore be avoided, and gentle starting up of the brake servo upon actuation can be realized.
In order to ensure complete restoring of the brake servo into a standby position, the means are preferably provided in a defined, leaky manner.
The means can be integrated into the known construction of a brake servo in a simple way without extensive modifications, by the means preferably being arranged circumferentially on the rolling diaphragm or the control housing, and by, at the beginning of the actuation, the means separating the main chamber from the prechamber in a defined, leaky manner by bearing against the servo housing or an intermediate floor.
One alternative embodiment of the invention provides that the means are arranged circumferentially on the servo housing, and that, at the beginning of the actuation, the means separate the main chamber from the prechamber in a defined, leaky manner by bearing against the rolling diaphragm.
A circumferential lip is preferably formed integrally as means on the rolling diaphragm, which circumferential lip bears against the servo housing or the intermediate floor at the beginning of actuation. Here, the lip can already be provided in a simple way during the production of the rolling diaphragm.
According to one advantageous development, in order not to endanger the functionality of the brake servo, at least one rib is provided on the circumferential lip, which rib ensures the defined leakiness of the lip. Here, a modification of the servo housing is advantageously not necessary.
One alternative, advantageous embodiment of the invention provides that the circumferential lip has at least one recess which ensures the defined leakiness of the lip, a modification of the servo housing not being necessary here either.
According to one advantageous embodiment of the invention, a reversibly deformable, circumferential filter element which ventilates the main chamber in a throttled manner at the beginning of the actuation can be provided as means.
At least one channel is preferably provided in the bearing region of the means, which channel ensures the defined leakiness of the means. Depending on the arrangement of the means, the channel can be provided on the servo housing or on the movable wall.
According to one advantageous embodiment, the filter element has at least one passage channel which ensures the defined leakiness of the filter element. No modification of the servo housing is necessary in this embodiment of the invention either.
One advantageous embodiment provides that the means are arranged in the region of an axial section of the servo housing, as a result of which the prechamber can be of small configuration at the beginning of the actuation.
According to a further advantageous embodiment of the invention, the means are arranged in the region of a radial flange section of the servo housing.
If, according to another advantageous embodiment, the means are arranged in the region of an oblique section of the servo housing, the brake servo can also have what is known as a tie rod.